1. Field of the Invention
The present invention relates to a heat-treating apparatus for processing a substrate placed on a hot plate by a heating process, a heat-treating method, and a storage medium storing a program including instructions for carrying out the heat-treating method.
2. Description of the Related Art
A heat-treating apparatus is incorporated into a coating and developing system for processing a substrate by wet processes, such as a coating process for coating a substrate with a resist film and a developing process for processing a substrate coated with a resist film. The heat-treating apparatus processes substrates respectively coated with resist films of different kinds. Therefore, heat-treating conditions including a proper heating temperature and a proper heating time are selectively determined in compliance with the kinds of resist films.
For example, when a heating temperature to be used by the heat-treating apparatus for the succeeding lot of substrates is different from that used by the heat-treating apparatus for the preceding lot of substrates, the heat-treating apparatus is set for the heating temperature for the succeeding lot of substrates. For example, when the heating temperature for the succeeding lot of substrates is higher than that for the preceding lot of substrates, the output of a heater incorporated into a heating plate is increased. When the heating temperature for the succeeding lot of substrates is lower than that for the preceding lot of substrates, the heating plate is cooled.
Cooling methods of cooling the heating plate mentioned in, for example, JP-A H10-284382 (Paragraph [0012], FIG. 1) and JP-A 2001-52985 (Paragraphs (0013) and [0031]) bring the lower surface of the heating plate into contact with a flowing coolant, such as a flowing liquid, to cool the heating plate through heat exchange between the heating plate and the coolant. When the heating plate is cooled by those cooling methods, a passage is defined for the coolant to circulate the coolant through a space contiguous with the back surfaces of the heating plate and a cooling mechanism for cooling the coolant to avoid contaminating the surface of the heating plate with the coolant.
The heating plate is made of a high-strength material, such as aluminum nitride (AlN) and has a small thickness on the order of, for example, 3 mm. While on the one hand such a material has high strength, the material is expensive and requires a high machining cost. Efforts have been made in recent years to use an inexpensive metal not requiring high machining cost, such as aluminum (Al), instead of the foregoing expensive material. Aluminum, as compared with aluminum nitride, has a low strength and hence the heating plate of aluminum needs to be formed in a big thickness that will not allow the heating plate to warp to provide the heating plate with a necessary strength. Increase in the thickness of the heating plate increases the heat capacity of the heating plate. When lots are changed, the heating plate having a large heat capacity takes a long time for cooling, which reduces throughput.
The thick heating plate may be cooled in a short cooling time by increasing the flow of the coolant for cooling the heating plate. However, the coating and developing system is designed such that cooling can be achieved by circulating the coolant at the lowest possible flow rate. Therefore, a small cooling device, such as a small compressor for compressing a cooling gas, a small booster pump for supplying cooling water or a small chiller, having a capacity sufficient to supply the coolant at a necessary flow rate is employed. If the flow rate of the coolant needs to be increased, the design of the coating and developing system need to be changed to employ a large cooling device. Thus, it has been very difficult to reduce the cooling time.
On the other hand, it is desired to reduce the flow of the coolant supplied by the cooling device without increasing the cooling time necessary for cooling the heating plate to reduce electric energy necessary for supplying the coolant or to reduce the size of the cooling device.
As mentioned above, the heat treatment of the succeeding lot of substrates is started immediately after cooling the heating plate and hence the surface of the heating plate needs to be cooled uniformly. For example, nozzles for spouting a coolant on the cooling plate needs to be placed at many positions relative to the heating plate and many supply lines need to be connected to the nozzles to cool the heating plate uniformly. Consequently, the component parts, the size and the cost of the heat-treating apparatus increase.